The present invention relates to an image processing devices; and, more particularly, to an apparatus and method for automatically controlling an exposure time using a mean value of green pixels in an image sensor, reducing a burden of hardware and software and improving a performance of the image sensor.
A conventional image sensor has controlled an illuminance of image using software. Software calculates a current illuminance using a captured image value. Then, if the calculated illuminance is judged to be very bright or very dark, an external controller adjusts the illuminance of the image. Thereafter, illuminance of the adjusted image is again read to judge the illuminance of the image.
In such a conventional method for controlling illuminance through software, however, the actual judgement of the illuminance is completed after processing at least two images from the image sensor. Therefore, a problem may occur and the software is burdened with an increased amount of calculation. In addition, the calculated results should be again programmed through a programming interface and the programmed results is applied to the image capturing, so that a considerable delay time is required. Furthermore, in case the image sensor is used in such as CCTV (Closed Circuit Television), where it is difficult for software to control the illuminance, it may not cope with the change of situation initially set up.
It is, therefore, an object of the present invention to provide an apparatus and method for automatically controlling exposure time using an green pixel value in an image sensor, reducing a burden of hardware and software and improving a performance of the image sensor.
In accordance with an embodiment of present invention, there is provided a method for automatically controlling an exposure time using a mean value of green pixels in image sensor, wherein the image sensor includes a pixel array, the method comprising the steps of a) producing total pixel value of the green pixels from the pixel array; b) producing a mean value of the green pixels dividing the total pixel value of the green pixels by the number of the green pixels; c) producing a deviation value, wherein the deviation value is an absolute value of a difference between the mean value and a predetermined reference value; d) comparing the deviation value with a predetermined boundary value; e) in case where the deviation value is smaller than the predetermined boundary value, capturing a next image according to a current exposure time, and in case where the deviation value is larger than the predetermined boundary value, calculating an exposure control rate and determining whether an automatic exposure control mode is enabled; and f) in case where the automatic exposure control mode is disabled, capturing the next image according to the current exposure time, and in case where the automatic exposure control mode is enabled, capturing the next image according a next exposure time, wherein the next exposure time is calculated multiplying the current exposure time by the exposure control rate.
In accordance with another embodiment of the present invention, there is provided an image sensor for automatically control an exposure time using a mean value of green pixels, comprising; a) an operation means for receiving a size of window in window mode, green pixel values from a plurality of the green pixels, a current exposure time and a predetermined reference value to perform an addition and shift operation in response to a control signal; b) a storage means for storing an operation results from the operation means in response to a clock signal; c) an operation control means for receiving the operation results from the storage means, an area of the window for calculating the number of the green pixels in window mode and a line number to output the control signal, wherein the operation results include a updated exposure time, an exposure control rate, a mean value of the green pixels and the number of the green pixels; d) an update determination means for determining whether to update an exposure time and outputting an updating signal in response to the predetermined reference value, an predetermined boundary value and the mean value of the green pixels from the storage means; and e) an exposure time generating means for receiving the new exposure time and outputting the updated exposure time as a next exposure time of next image in response to the updating signal from the update determination means and an automatic exposure control mode.